Mast cells in rat thalamus: nuclear localization, sex difference and left-right asymmetry

Is there something sexual in the ventral midline thalamus?

This mini-review explores sexual dimorphism in the ventral midline thalamus, focusing on the reuniens nucleus and its role in behavioral functions. Traditionally linked to tasks such as working memory, cognitive flexibility, fear generalization, and memory consolidation, most studies have been conducted in male rodents. Research comparing the effects of ventral midline thalamus manipulations between female and male rodents is limited. Emerging evidence suggests sex-specific differences, particularly in response to stress, pharmacological manipulations, and memory processes. Studies reveal distinct c-Fos expression patterns in the reuniens nucleus between females and males, especially under stress, with females often showing different neural activation. Additionally, females exhibit different recruitment of the reuniens nucleus in object recognition tasks, indicating possible sex-dependent cognitive strategies. While evidence suggests functional differences between sexes in the reuniens nucleus, current data are limited. Further research is needed to understand how sex influences brain function and cognition, particularly in the ventral midline thalamus, which is crucial for various cognitive processes.

In humans, striato-pallido-thalamic projections are largely segregated by their origin in either the striosome-like or matrix-like compartments

Cortico-striato-thalamo-cortical (CSTC) loops are fundamental organizing units in mammalian brains. CSTCs process limbic, associative, and sensorimotor information in largely separated but interacting networks. CTSC loops pass through paired striatal compartments, striosome (aka patch) and matrix, segregated pools of medium spiny projection neurons with distinct embryologic origins, cortical/subcortical structural connectivity, susceptibility to injury, and roles in behaviors and diseases. Similarly, striatal dopamine modulates activity in striosome and matrix in opposite directions. Routing CSTCs through one compartment may be an anatomical basis for regulating discrete functions. We used differential structural connectivity, identified through probabilistic diffusion tractography, to distinguish the striatal compartments (striosome-like and matrix-like voxels) in living humans. We then mapped compartment-specific projections and quantified structural connectivity between each striatal compartment, the globus pallidus interna (GPi), and 20 thalamic nuclei in 221 healthy adults. We found that striosome-originating and matrix-originating streamlines were segregated within the GPi: striosome-like connectivity was significantly more rostral, ventral, and medial. Striato-pallido-thalamic streamline bundles that were seeded from striosome-like and matrix-like voxels transited spatially distinct portions of the white matter. Matrix-like streamlines were 5.7-fold more likely to reach the GPi, replicating animal tract-tracing studies. Striosome-like connectivity dominated in six thalamic nuclei (anteroventral, central lateral, laterodorsal, lateral posterior, mediodorsal-medial, and medial geniculate). Matrix-like connectivity dominated in seven thalamic nuclei (centromedian, parafascicular, pulvinar-anterior, pulvinar-lateral, ventral lateral-anterior, ventral lateral-posterior, ventral posterolateral). Though we mapped all thalamic nuclei independently, functionally-related nuclei were matched for compartment-level bias. We validated these results with prior thalamostriate tract tracing studies in non-human primates and other species; where reliable data was available, all agreed with our measures of structural connectivity. Matrix-like connectivity was lateralized (left > right hemisphere) in 18 thalamic nuclei, independent of handedness, diffusion protocol, sex, or whether the nucleus was striosome-dominated or matrix-dominated. Compartment-specific biases in striato-pallido-thalamic structural connectivity suggest that routing CSTC loops through striosome-like or matrix-like voxels is a fundamental mechanism for organizing and regulating brain networks. Our MRI-based assessments of striato-thalamic connectivity in humans match and extend the results of prior tract tracing studies in animals. Compartment-level characterization may improve localization of human neuropathologies and improve neurosurgical targeting in the GPi and thalamus.

Systemic mastocytosis: The roles of histamine and its receptors in the central nervous system disorders

Mastocytosis is a rare disease of clonal hematological disorders characterized by a pathological accumulation of Mast Cells (MCs) in different tissues, with variable symptomatology and prognosis. Signs and symptoms of Systemic Mastocytosis (SM) are due to pathological infiltration of MCs and to the release of chemical mediators, mainly histamine. Patients with SM may also present with neurological symptoms or complications. The pathophysiology of these neurological disorders remains uncertain to this day, but it can be associated with the infiltration of tissue mastocytes, release of mastocytes' mediators or both. Moreover, there is a lot to understand about the role of neurological symptoms in SM and knowing, for example, what is the real frequency of neurological disorders in SM and if is present a relation between other SM subtypes, because it has been noted that the alteration of the histamine expression may be an initiating factor for susceptibility, gravity and progression of the epigenetic disease. In this review we explain the possible pathophysiological mechanism about neurological symptomatology found in some patients affected by SM, describing the role of histamine and its receptors in the nervous system and, in light of the results, what the future prospects may be for a more specific course of treatment.

Mast Cells, Stress, Fear and Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a developmental condition characterized by impaired communication and obsessive behavior that affects 1 in 59 children. ASD is expected to affect 1 in about 40 children by 2020, but there is still no distinct pathogenesis or effective treatments. Prenatal stress has been associated with higher risk of developing ASD in the offspring. Moreover, children with ASD cannot handle anxiety and respond disproportionately even to otherwise benign triggers. Stress and environmental stimuli trigger the unique immune cells, mast cells, which could then trigger microglia leading to abnormal synaptic pruning and dysfunctional neuronal connectivity. This process could alter the "fear threshold" in the amygdala and lead to an exaggerated "fight-or-flight" reaction. The combination of corticotropin-releasing hormone (CRH), secreted under stress, together with environmental stimuli could be major contributors to the pathogenesis of ASD. Recognizing these associations and preventing stimulation of mast cells and/or microglia could greatly benefit ASD patients.

Mast cell-neural interactions contribute to pain and itch

Mast cells are best recognized for their role in allergy and anaphylaxis, but increasing evidence supports their role in neurogenic inflammation leading to pain and itch. Mast cells act as a "power house" by releasing algogenic and pruritogenic mediators, which initiate a reciprocal communication with specific nociceptors on sensory nerve fibers. Consequently, nerve fibers release inflammatory and vasoactive neuropeptides, which in turn activate mast cells in a feedback mechanism, thus promoting a vicious cycle of mast cell and nociceptor activation leading to neurogenic inflammation and pain/pruritus. Mechanisms underlying mast cell differentiation, activation, and intercellular interactions with inflammatory, vascular, and neural systems are deeply influenced by their microenvironment, imparting enormous heterogeneity and complexity in understanding their contribution to pain and pruritus. Neurogenic inflammation is central to both pain and pruritus, but specific mediators released by mast cells to promote this process may vary depending upon their location, stimuli, underlying pathology, gender, and species. Therefore, in this review, we present the contribution of mast cells in pathological conditions, including distressing pruritus exacerbated by psychologic stress and experienced by the majority of patients with psoriasis and atopic dermatitis and in different pain syndromes due to mastocytosis, sickle cell disease, and cancer.

Targeting mast cell as a neuroprotective strategy

Background: Mast cells (MCs) are perivascularly located immune cells of haematopoietic origin. Emerging evidences suggest that the activation of MCs play important roles in the pathogenesis of blood brain barrier disruption, neuroinflammation, and neurodegeneration. Objectives: In this review, we aimed to discuss the detrimental effects of MCs in response to various types of brain injury, as well as the therapeutic potential and neuroprotective effects of targeting the activation and degranulation of MCs, particularly in the management of the acute phase. Methods: An extensive online literature search was conducted through Pubmed/Central on March 2018. Then, we comprehensively summarized the effects of the activation of brain MCs in acute brain injury along with current pharmacological strategies targeting at the activation of MCs. Results: The review of the current literature indicated that the activation and degranulation of brain MCs significantly contribute to the acute pathological process following different types of brain injury including focal and global cerebral ischaemia, intracerebral haemorrhage, subarachnoid haemorrhage, and traumatic brain injury. Conclusions: Brain MCs significantly contribute to the acute pathological processes following brain injury. In that regard, targeting brain MCs may provide a novel strategy for neuroprotection.

Effects of Mycotoxins on Neuropsychiatric Symptoms and Immune Processes

PURPOSE

The effects of air pollutants have been receiving increased attention both clinically and in the media. One such pollutant is mold, fungal growth in the form of multicellular filaments known as hyphae. The growth of molds is omnipresent not only in outdoor settings but also in indoor environments containing excessive amounts of moisture.

METHODS

PubMed was searched for relevant articles using terms such as mold, mycotoxins, fungi, immunity, inflammation, neurodevelopment, cognition, Alzheimer's, and autism.

FINDINGS

Exposure to molds is most commonly associated with allergies and asthma. However, it is now thought to be associated with many complex health problems, since some molds, especially Trichoderma, Fusarium and Stachybotrys spp, produce mycotoxins that are absorbed from the skin, airways, and intestinal lining. People exposed to molds and mycotoxins present with symptoms affecting multiple organs, including the lungs, musculoskeletal system, as well as the central and peripheral nervous systems. Furthermore, evidence has recently implicated exposure to mycotoxins in the pathogenesis of autism spectrum disorder. The effects of mycotoxins can be mediated via different pathways that include the secretion of pro-inflammatory cytokines, especially from mast cells.

IMPLICATIONS

The information reviewed indicates that exposure to mold and mycotoxins can affect the nervous system, directly or through immune cell activation, thus contributing to neurodevelopmental disorders such as autism spectrum disorder.

Proceedings of the 2017 National Toxicology Program Satellite Symposium

The 2017 annual National Toxicology Program Satellite Symposium, entitled "Pathology Potpourri," was held in Montreal, Quebec, Canada at the Society of Toxicologic Pathology's 36th annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were used by the audience for voting and discussion. Various lesions and other topics covered during the symposium included renal papillary degeneration in perinatally exposed animals, an atriocaval mesothelioma, an unusual presentation of an alveolar-bronchiolar carcinoma, a paraganglioma of the organ of Zuckerkandl (also called an extra-adrenal pheochromocytoma), the use of human muscle samples to illustrate the challenges of manual scoring of fluorescent staining, intertubular spermatocytic seminomas, medical device pathology assessment and discussion of the approval process, collagen-induced arthritis, incisor denticles, ameloblast degeneration and poorly mineralized enamel matrix, connective tissue paragangliomas, microcystin-LR toxicity, perivascular mast cells in the forebrain thalamus unrelated to treatment, and 2 cases that provided a review of the International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) bone nomenclature and recommended application of the terminology in routine nonclinical toxicity studies.

Thalamic mast cell activity is associated with sign-tracking behavior in rats

Mast cells are resident immune cells in the thalamus that can degranulate and release hundreds of signaling molecules (i.e., monoamines, growth factors, and cytokines) both basally and in response to environmental stimuli. Interestingly, mast cell numbers in the brain show immense individual variation in both rodents and humans. We used a Pavlovian conditioned approach (PCA) procedure to examine whether mast cells are associated with individual variation in the attribution of incentive-motivational value to reward-related cues. During the PCA procedure, a lever response-independently predicts the delivery of a food pellet into a magazine, and over training sessions three conditioned responses (CRs) develop: sign-tracking (lever-directed CRs), goal-tracking (magazine-directed CRs), and an intermediate response (both CRs). In Experiment 1, we measured thalamic mast cell number/activation using toluidine blue and demonstrated that sign-trackers have increased degranulated (activated) but not granulated (inactive) mast cells. In Experiment 2, we infused the mast cell inhibitor, cromolyn (200µg/rat; i.c.v.), immediately before five daily PCA training sessions and demonstrated that mast cell inhibition selectively impairs the acquisition of sign-tracking behavior. Taken together, these results demonstrate that thalamic mast cells contribute to the attribution of incentive-motivational value to reward-related cues and suggest that mast cell inhibition may be a novel target for addiction treatment.

Immunoregulatory effect of mast cells influenced by microbes in neurodegenerative diseases

When related to central nervous system (CNS) health and disease, brain mast cells (MCs) can be a source of either beneficial or deleterious signals acting on neural cells. We review the current state of knowledge about molecular interactions between MCs and glia in neurodegenerative diseases such as Multiple Sclerosis, Alzheimer's disease, Amyotrophic Lateral Sclerosis, Parkinson's disease, Epilepsy. We also discuss the influence on MC actions evoked by the host microbiota, which has a profound effect on the host immune system, inducing important consequences in neurodegenerative disorders. Gut dysbiosis, reduced intestinal motility and increased intestinal permeability, that allow bacterial products to circulate and pass through the blood-brain barrier, are associated with neurodegenerative disease. There are differences between the microbiota of neurologic patients and healthy controls. Distinguishing between cause and effect is a challenging task, and the molecular mechanisms whereby remote gut microbiota can alter the brain have not been fully elucidated. Nevertheless, modulation of the microbiota and MC activation have been shown to promote neuroprotection. We review this new information contributing to a greater understanding of MC-microbiota-neural cells interactions modulating the brain, behavior and neurodegenerative processes.

Evidence for the modulation of nociception in mice by central mast cells

BACKGROUND

Hyperalgesia that develops following nerve ligation corresponds temporally and in magnitude with the number of thalamic mast cells located contralateral to the ligature. We tested the possibility that mast cells modulate nociception centrally, similar to their role in the periphery.

METHODS

We examined the central effect of two hyperalgesic compounds that induce mast cell degranulation and of stabilized mast cells using cromolyn.

RESULTS

Thermal hyperalgesia (tail flick) induced by nerve growth factor (NGF, a neurotrophic compound) and mechanical hyperalgesia (von Frey) induced by dynorphin A (1-17) (opioid compound) each correlated with the per cent of thalamic mast cells that were degranulated. Degranulation of these mast cells by the central injection of compound 48/80, devoid of neurotrophic or opioid activity, was sufficient to recapitulate thermal hyperalgesia. Stabilization of mast cells by central injections of cromolyn produced no analgesic effect on baseline tail flick or von Frey fibre sensitivity, but inhibited thermal hyperalgesia produced by compound 48/80 and tactile hyperalgesia induced by dynorphin and by Freund's complete adjuvant. Finally, chemical nociception produced by the direct activation of nociceptors by formalin (phase I) was not inhibited by centrally injected cromolyn whereas chemical nociception dependent on central sensitization (formalin-phase II and acetic acid-induced abdominal stretches) was.

CONCLUSIONS

These convergent lines of evidence suggest that degranulation of centrally located mast cells sensitizes central nociceptive pathways leading to hyperalgesia and tonic chemical sensitivity.

SIGNIFICANCE

Hyperalgesia induced by spinal nerve ligation corresponds temporally and in magnitude with degranulation of thalamic mast cells. Here, we provide evidence that hyperalgesia induced by NGF, formalin and dynorphin also may depend on mast cell degranulation in the CNS whereas cromolyn, a mast cell stabilizer, blocks these effects in mice.

Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.

Mastocytosis in adulthood and neuropsychiatric disorders

Patients with mastocytosis can display various disabling general and neuropsychological symptoms among one third of them, including general signs such as fatigue and musculoskeletal pain, which can have a major impact on quality of life. Neurological symptoms are less frequent and mainly consist of acute or chronic headache (35%), rarely syncopes (5%), acute onset back pain (4%), and in a few cases, clinical and radiological symptoms resembling or allowing the diagnosis of multiple sclerosis (1.3%). Headaches are associated with symptoms related to mast cell activation syndrome (flushes, prurit, and so forth) and more frequently present as migraine (37.5%), with often aura (66%). Depression-anxiety like symptoms can occur in 40% to 60% of the patients and cognitive impairment is not rare (38.6%). The pathophysiology of these symptoms could be linked to tissular mast cell infiltration or to mast cell mediators release or both. The tryptophan metabolism could be involved in mast cell-induced neuroinflammation through indoleamine-2,3-dioxygenase activation. Treatments targeting mast cell may be useful to target neuropsychological features associated with mastocytosis, including tyrosine kinase inhibitors.

Meningeal mast cell-T cell crosstalk regulates T cell encephalitogenicity

GM-CSF is a cytokine produced by T helper (Th) cells that plays an essential role in orchestrating neuroinflammation in experimental autoimmune encephalomyelitis, a rodent model of multiple sclerosis. Yet where and how Th cells acquire GM-CSF expression is unknown. In this study we identify mast cells in the meninges, tripartite tissues surrounding the brain and spinal cord, as important contributors to antigen-specific Th cell accumulation and GM-CSF expression. In the absence of mast cells, Th cells do not accumulate in the meninges nor produce GM-CSF. Mast cell-T cell co-culture experiments and selective mast cell reconstitution of the meninges of mast cell-deficient mice reveal that resident meningeal mast cells are an early source of caspase-1-dependent IL-1β that licenses Th cells to produce GM-CSF and become encephalitogenic. We also provide evidence of mast cell-T cell co-localization in the meninges and CNS of recently diagnosed acute MS patients indicating similar interactions may occur in human demyelinating disease.

Evidencing different neurochemical profiles between thalamic nuclei using high resolution 2D-PRESS semi-LASER (1)H-MRSI at 7 T

OBJECTIVE

To demonstrate that high resolution (1)H semi-LASER MRSI acquired at 7 T permits discrimination of metabolic patterns of different thalamic nuclei.

MATERIALS AND METHODS

Thirteen right-handed healthy volunteers were explored at 7 T using a high-resolution 2D-semi-LASER (1)H-MRSI sequence to determine the relative levels of N-Acetyl Aspartate (NAA), choline (Cho) and creatine-phosphocreatine (Cr) in eight VOIs (volume <0.3 ml) centered on four different thalamic nuclei located on the Oxford thalamic connectivity atlas. Post-processing was done using the CSIAPO software. Chemical shift displacement of metabolites was evaluated on a phantom and correction factors were applied to in vivo data.

RESULTS

The global assessment (ANOVA p < 0.05) of the neurochemical profiles (NAA, Cho and Cr levels) with thalamic nuclei and hemispheres as factors showed a significant global effect (F = 11.98, p < 0.0001), with significant effect of nucleus type (p < 0.0001) and hemisphere (p < 0.0001). Post hoc analyses showed differences in neurochemical profiles between the left and the right hemisphere (p < 0.05), and differences in neurochemical profiles between nuclei within each hemisphere (p < 0.05).

CONCLUSION

For the first time, using high resolution 2D-PRESS semi-LASER (1)H-MRSI acquired at 7 T, we demonstrated that the neurochemical profiles were different between thalamic nuclei, and that these profiles were dependent on the brain hemisphere.

Mast cell and autoimmune diseases

Mast cells are important in innate immune system. They have been appreciated as potent contributors to allergic reaction. However, increasing evidence implicates the important role of mast cells in autoimmune disease like rheumatoid arthritis and multiple sclerosis. Here we review the current stage of knowledge about mast cells in autoimmune diseases.

Leukocyte telomere length in mastocytosis: correlations with depression and perceived stress

BACKGROUND

Mastocytosisis a rare disease associated with chronic symptoms related to mast cell mediator release. Patients with mastocytosis display high level of negative emotionality such as depression and stress sensibility. Brain mast cells are mainly localized in the diencephalon, which is linked to emotion regulatory systems. Negative emotionality has been shown to be associated with telomere shortening. Taken together these observations led us to hypothesize that mast cells activity could be involved in both negative emotionality and telomere shortening in mastocytosis.

OBJECTIVE

To demonstrate a possible relationship between negative emotionality in mastocytosis and leukocytes telomere length.

METHODS

Leukocyte telomere length and telomerase activity were measured among mastocytosis patients and were correlated with perceived stress and depression assessed by the Beck Depression Inventory revised and the Perceived Stress Scale.

RESULTS

Mild-severe depression scores were frequent (78.9%) as well as high perceived stress (42.11%). Telomere length was correlated to perceived stress (r=0.77; p=0.0001) but not to depression in our population. Patients displaying Wild-type KIT significantly presented higher perceived stress levels. Patients with the D816VC KIT mutation who had high perceived stress scores displayed significantly shorter telomere but not if they had high depression scores.

CONCLUSION

These findings suggest that high perceived stress in mastocytosis could accelerate the rate of leukocytes telomere shortening. Since mastocytosis is, by definition, a mast cell mediated disease; these cells could be involved in this phenomenon. Mechanistic causal relationships between these parameters need to be investigated.

Effect of hyperthermia on histamine blood level and convulsive behavior in infant rats

Febrile seizures (FS), which have been extensively studied using animal models, are the most common type of convulsive events in children, but the cellular mechanisms causing FS are still unclear. Histamine has been suggested to participate in seizure control. This study investigated the effect of hyperthermia (HT) on histamine blood level (HBL) and convulsive behavior in prepubertal rats. Forty Wistar rat pups were assigned to 5 groups (n=8), namely, control, HT, cromolyn, chlorpheniramine, and ranitidine. Two groups of adult rats were also used as control and HT adults. The control rats were placed in a hyperthermic chamber, and a room temperature current of air was blown on them. In all other groups, the rats were placed in the chamber for 30 min, and a current of warm air was applied to them. In the pretreatment groups, the rats received an injection of 68-mg/kg cromolyn sodium, 4-mg/kg chlorpheniramine, or 80-mg/kg ranitidine intraperitoneally 30 min prior to HT. Body temperature and convulsive behaviors were recorded. Then, the rats were anesthetized with ether, and their blood sample was obtained through direct heart puncture. Hyperthermia initiated convulsive behaviors in infant rats but not in the adult ones. Pretreatment with chlorpheniramine significantly potentiated convulsive behaviors (p=0.017). Hyperthermia led to a significant decrease in the HBL of both infant (p<0.001) and adult (p=0.003) rats. Pretreatments led to more decrease in the HBL of infant rats (p<0.001). It was concluded that HT could lead to a decrease in HBL, which in turn increases the seizure susceptibility of animals. Histamine may have a pivotal role in hyperthermia-induced seizures.

A focus on mast cells and pain

Mast cells (MCs) are immunocytes with secretory functions that act locally in peripheral tissues to modulate local hemodynamics, nociceptor activation and pain. They are also able to infiltrate the central nervous system (CNS), especially the spinal cord and the thalamus, but their cerebral function remains an enigma. A role in regulating the opening of the blood-brain barrier has been proposed. Paracrine-like action of MCs on synaptic transmission might also signal a modulation of the nervous system by the immune system. In this review, we examine the link between MCs and nociceptive process, at the periphery as well as in the CNS.

Central nervous system mast cells in peripheral inflammatory nociception

BACKGROUND

Functional aspects of mast cell-neuronal interactions remain poorly understood. Mast cell activation and degranulation can result in the release of powerful pro-inflammatory mediators such as histamine and cytokines. Cerebral dural mast cells have been proposed to modulate meningeal nociceptor activity and be involved in migraine pathophysiology. Little is known about the functional role of spinal cord dural mast cells. In this study, we examine their potential involvement in nociception and synaptic plasticity in superficial spinal dorsal horn. Changes of lower spinal cord dura mast cells and their contribution to hyperalgesia are examined in animal models of peripheral neurogenic and non-neurogenic inflammation.

RESULTS

Spinal application of supernatant from activated cultured mast cells induces significant mechanical hyperalgesia and long-term potentiation (LTP) at spinal synapses of C-fibers. Lumbar, thoracic and thalamic preparations are then examined for mast cell number and degranulation status after intraplantar capsaicin and carrageenan. Intradermal capsaicin induces a significant percent increase of lumbar dural mast cells at 3 hours post-administration. Peripheral carrageenan in female rats significantly increases mast cell density in the lumbar dura, but not in thoracic dura or thalamus. Intrathecal administration of the mast cell stabilizer sodium cromoglycate or the spleen tyrosine kinase (Syk) inhibitor BAY-613606 reduce the increased percent degranulation and degranulated cell density of lumbar dural mast cells after capsaicin and carrageenan respectively, without affecting hyperalgesia.

CONCLUSION

The results suggest that lumbar dural mast cells may be sufficient but are not necessary for capsaicin or carrageenan-induced hyperalgesia.

Neuro-immune interactions in the dove brain

Mast cells (MC) are of hematopoetic origin. Connective tissue type MCs are able to function in IgE dependent and independent fashion, change their phenotype according to the tissue environment. They are able to enter the brain under normal physiological conditions, and move into this compact tissue made of neurons. In doves MCs are found only in the medial habenula (MH) and their number is changing according to the amount of sex steroids in the body. MCs are able to synthesize and store a great variety of biologically active compounds, like transmitters, neuromodulators and hormones. They are able to secrete GnRH. With the aid of electron microscopy we were able to describe MC-neuron interactions between GnRH-positive MCs and neurons. Piecemeal degranulation (secretory vesicles budding off swollen and active granules) seems to be a very efficient type of communication between MCs and surrounding neurons. Different types of granular and vesicular transports are seen between GnRH-immunoreactive MCs and neurons in the MH of doves. Sometimes whole granules are visible in the neuronal cytoplasm, in other cases exocytotic vesicles empty materials of MC origin. Thus MCs might modulate neuronal functions. Double staining experiments with IP3-receptor (IP3R), Ryanodine-receptor (RyR) and serotonin antibodies showed active MC population in the habenula. Light IP3R-labeling was present in 64-97% of the cells, few granules were labeled in 7-10% of MCs, while strong immunoreactivity was visible in 1-2% of TB stained cells. No immunoreactivity was visible in 28-73% of MCs. According to cell counts, light RyR-positivity appeared in 27-52%, few granules were immunoreactive in 4-19%, while strong immunopositivity was found only in one animal. In this case 22% of MCs were strongly RyR-positive. No staining was registered in 44-73% of MCs. Double staining with 5HT and these receptor markers proved that indeed only a part of MCs is actively secreting. Resting cells with only 5HT-immunopositivity are often visible. The activational state of MCs is changing at higher estrogen/testosterone level, thus with the secretion of neuromodulators they might alter sexual and parental behavior of the animals.

Spontaneous locomotor activity correlates with the degranulation of mast cells in the meninges rather than in the thalamus: disruptive effect of cocaine

Mast cells are located in the central nervous system (CNS) of many mammals and stress induces their degranulation. We postulated that mast cells are associated with wakefulness and stimulatory tone in the CNS, as reflected by spontaneous motor activity. Because stress also precipitates drug-seeking behavior in cocaine addicts, we also postulated that cocaine manifests its effects through this relationship. We investigated the influence of single and repeated injections of cocaine on circulating corticosterone, motor activity and degranulation of mast cells in both the thalamus and meninges of mice. Mice were subjected to 5 consecutive days of cocaine or saline followed by a single injection of cocaine or saline 11 days later. Spontaneous locomotor activity was measure for 1h after the final injection before death. Neither a single injection nor prior treatment with cocaine increased motor activity compared to saline-injected controls, however, repeated administration of cocaine induced a significant sensitization to its behavioral effect when delivered 11 days later. In mice that received only saline, motor activity correlated positively with mast cell degranulation in the meninges but not in the thalamus. Cocaine, regardless of the treatment schedule, disrupted this correlation. The concentration of corticosterone did not differ amongst groups and did not correlate with either behavior or mast cell parameters in any group. The correlation between behavioral activity and the mast cell degranulation in the meninges suggests that these parameters are linked. The disruptive effect of cocaine on this relationship indicates a role downstream from mast cells in the regulation of motor activity.

Mast cells as early responders in the regulation of acute blood-brain barrier changes after cerebral ischemia and hemorrhage

The inflammatory response triggered by stroke has been viewed as harmful, focusing on the influx and migration of blood-borne leukocytes, neutrophils, and macrophages. This review hypothesizes that the brain and meninges have their own resident cells that are capable of fast host response, which are well known to mediate immediate reactions such as anaphylaxis, known as mast cells (MCs). We discuss novel research suggesting that by acting rapidly on the cerebral vessels, this cell type has a potentially deleterious role in the very early phase of acute cerebral ischemia and hemorrhage. Mast cells should be recognized as a potent inflammatory cell that, already at the outset of ischemia, is resident within the cerebral microvasculature. By releasing their cytoplasmic granules, which contain a host of vasoactive mediators such as tumor necrosis factor-alpha, histamine, heparin, and proteases, MCs act on the basal membrane, thus promoting blood-brain barrier (BBB) damage, brain edema, prolonged extravasation, and hemorrhage. This makes them a candidate for a new pharmacological target in attempts to even out the inflammatory responses of the neurovascular unit, and to stabilize the BBB after acute stroke.

An emerging role of mast cells in cerebral ischemia and hemorrhage

Mast cells (MCs) are perivascularly located resident cells of hematopoietic origin, recognized as effectors in inflammation and immunity. Their subendothelial location at the boundary between the intravascular and extravascular milieus, and their ability to rapidly respond to blood- and tissue-borne stimuli via release of potent vasodilatatory, proteolytic, fibrinolytic, and proinflammatory mediators, render MCs with a unique status to act in the first-line defense in various pathologies. We review experimental evidence suggesting a role for MCs in the pathophysiology of brain ischemia and hemorrhage. In new-born rats, MCs contributed to brain damage in hypoxic-ischemic insults. In experimental cerebral ischemia/reperfusion, MCs regulated permeability of the blood-brain barrier, brain edema formation, and the intensity of local neutrophil infiltration. MCs were reported to play a role in the tissue plasminogen activator-mediated cerebral hemorrhages after experimental ischemic stroke, and to be involved in the expansion of hematoma and edema following intracerebral hemorrhage. Importantly, the MC-stabilizing drug cromoglycate inhibited MC-mediated adverse effects on brain pathology and improved survival of experimental animals. This brings us to a position to consider MC stabilization as a novel initial adjuvant therapy in the prevention of brain injuries in hypoxia-ischemia in new-borns, as well as in ischemic stroke and intracerebral hemorrhage in adults.

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

Inflammation and the neurovascular unit in the setting of focal cerebral ischemia

Responses to focal cerebral ischemia by neurons and adjacent microvessels are rapid, simultaneous, and topographically related. Recent observations indicate the simultaneous appearance of proteases by components of nearby microvessels that are also expressed by neurons in the ischemic territory, implying that the events could be coordinated. The structural relationship of neurons to their microvascular supply, the direct functional participation of glial cells, and the observation of a highly ordered microvessel-neuron response to ischemia suggest that these elements are arranged in and behave in a unitary fashion, the neurovascular unit. Their roles as a unit in the stimulation of cellular inflammation and the generation of inflammatory mediators during focal cerebral ischemia have not been explored yet. However, components of the neurovascular unit both generate and respond to these influences under the conditions of ischemia. Here we briefly explore the potential inter-relationships of the components of the neurovascular unit with respect to their potential roles in ischemia-induced inflammatory responses.

Mast cells populations fluctuate along the spinal dura mater of the developing rat

The present study reveals developmental changes in the number, the phenotype and the distribution pattern of mast cells (MCs) along the cervical, the thoracic and the lumbar parts of the spinal dura mater. Postnatal infiltration of spinal dura by MCs does not appear to follow a sequential developmental pattern and meningeal MCs are unevenly distributed along the various parts of the examined dura. At each spinal level, areas most densely populated by MCs are the dorsal dura and the dural sleeves of the dorsal (sensory) spinal roots The developmental time course of the total MCs number is characterized by significant fluctuations in all three parts examined, with notable increases at P1, P4, P21 and P60 (peak value) for the cervical part, at P1 (peak value), P7 and P21 for the thoracic part and at P1, P7 (peak value) and P30 for the lumbar part. At P180, MCs number declines to 56%, 33% and 13% of the peak values for the cervical, the thoracic and the lumbar part, respectively. However, a different developmental pattern is followed by each subpopulation of MCs identified on the basis of their staining characteristics, namely connective tissue type mast cells (CTMCs), mucosal type or cells with characteristics of immature mast cells (MTMCs) and mixed type MCs, in each part examined. The findings may be of importance in elucidating physiological and pathological processes in the dura mater and the vertebral column.

Developmental changes of mast cell populations in the cerebral meninges of the rat

It is known that both the dura and the pia mater attract and support the differentiation of mast cells. The present study shows that unevenly distributed mast cells in the cerebral meninges of the rat can be found in perivascular sites and vessel ramification points, but can also be unrelated to the meningeal vasculature. It also documents changes in the number, localization and staining preferences of the mast cells in the two meninges of the developing and mature rat brain. Quantitative examination of all types of histochemically differentiated meningeal mast cells reveals no major (although some exist) differences between right and left side subpopulations, but strongly suggests a different origin and fate of the dural and the pial mast cells. The number of dural mast cells, already high from postnatal day 0, although declining from postnatal day 21 onwards, remains conspicuous up to postnatal day 180. In contrast, pial mast cells are comparatively very few in the first day of the postnatal life, and despite a transient significant increase in the following two weeks, they reach almost zero levels from postnatal day 21.

Mast cells as modulators of T-cell responses

Although mast cells have long been considered the integral effector cell in allergy and atopic disease, the paradigm of mast cell function is now evolving to incorporate data showing that mast cells make innumerable contributions to both protective and pathologic immune responses. Mast cells express cell surface molecules with costimulatory or co-inhibitory activity and produce a multitude of mediators that can direct dendritic cell (DC) or T-cell differentiation and function. In addition, mast cells exhibit a widespread distribution and are in close proximity to DCs and T cells at several critical sites. While there has been amazing progress in characterizing mast cell populations in vitro, only recently has the ability to monitor their in vivo effects become a reality. In this review, we discuss the evolution of our understanding of mast cell biology with an emphasis on their established and hypothesized roles in influencing T-cell differentiation and function. The fact that T-cell and mast cell interactions exist and are a normal component of most adaptive immune responses is one of the best illustrations of the now established concept that innate and adaptive immunity are not completely independent entities.

Mast cell-derived mediators protect against oxygen-glucose deprivation-induced injury in PC12 cells and neurons

Recent reports and our previous study suggest that mast cells play a crucial role in the pathological processes that follow cerebral ischemia. In this study, the effect of mast cells on neuron injury after cerebral ischemia was determined by adding in vitro ischemia-induced supernatant from mast cells to neurons and PC12 cells under the same conditions (oxygen-glucose deprivation, OGD). The degree of cell injury was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-dipheny-ltetrazolium bromide (MTT) assay. Mast cell-derived supernatant protected against OGD-induced injury of PC12 cells and neurons, and this protection was reversed by a histamine H1 antagonist and by anti-histamine serum, but not by an H2 antagonist. However, histamine and nerve growth factor (NGF) added separately or together did not have protective effects against OGD-induced injury. These results indicate that mast cell-derived protection during in vitro ischemia is histamine-dependent, and involves cooperation with other mediators, but not NGF.

Mast cells accumulate in the anogenital region of somatosensory thalamic nuclei during estrus in female mice

Mast cells are located in the mammalian thalamus where their numbers are sensitive to reproductive hormones. To evaluate whether differences between sexes and over the estrus cycle influence the nuclear distribution of mast cells in mice, we mounted a comprehensive analysis of their distribution in males compared to females and in females over the estrus cycle. Compared to males, mast cells were more numerous in the lateral intralaminar and posterior nuclei of females during estrus and in the ventral posterolateral (VPL) and medial geniculate nuclei during proestrus. During estrus, mast cells were especially concentrated in those regions within the VPL and posterior thalamic nuclei that receive somatosensory information from the anogenital region. Treatment of ovariectomized mice with estrogen increased the number and the percent of mast cells that were degranulated compared to that after ovariectomy alone, an effect that was most apparent in the lateral intralaminar, VPL and posterior nuclei. In estrogen-primed, ovariectomized females, progesterone delivered 5 h before tissue collection counteracted the effects of estrogen. Cromolyn, a mast cell stabilizer, injected centrally 1 h prior to and 24 h after estrogen in ovariectomized mice, prevented the increase in number of mast cells in the whole thalamus and in the intralaminar, VPL and posterior nuclei. This suggests that estrogen induces hyperplasia by a mechanism that involves mast cell degranulation. Based on the discrete anatomical location of mast cells in areas of somatosensory nuclei that receive anogenital input together with the temporal correspondence of these cells with estrus, mast cells are well situated to influence sensory input in females during mating.

The application of in vivo microiontophoresis for the investigation of mast cell-neuron interactions in the rat brain

Although mast cells are immune cells of hematopoietic origin, they can be found in parts of the central nervous system of many mammalian species. In the rat brain they are located in the thalamic region. Their function is not defined yet, although they are mostly known to secrete several chemicals, which may influence the surrounding neurons. There are no in vivo electrophysiological data available on the possible effects of brain mast cells on neurons. In this study, we used a combined method of microiontophoresis and extracellular single unit recording to simultaneously activate mast cells and record neuronal action potentials. Four-barrelled micropipettes were used for recording neuronal activity and for microiontophoretic application of mast cell degranulator Compound 48/80 (C48/80). Spike sorting routines were performed on-line and off-line to ensure that data were always recorded from a single neuron. C48/80 did not modify the firing rate of cortical neurons (no mast cells are found there), however, it caused excitation (n = 16/37, 43%), or inhibition (n = 9/37, 24%) in thalamic neurons possibly due to mast cell activation. Further investigations will clarify the biochemical nature of changes in neural excitability due to mast cell degranulation in the mammalian brain.

Mast cells modulate maintained neuronal activity in the thalamus in vivo

Single cell unit activity of 187 neurons of 24 rats were analysed to study the possible involvement of intracranial mast cells on modifying thalamic neuronal activity. Mast cells were activated with microiontophoretical application of compound 48/80. This substance did not modify the firing rate of cortical or hippocampal neurons (no mast cells are found here), however it caused excitation (70% in females, 11% in males), or inhibition (7% in females, 33% in males) on thalamic neurons, possibly due to mast cell activation. In consecutive anatomical evaluation many partially or fully degranulated mast cells were found in the recorded thalamic areas.

Differential effects of two analgesic drugs, morphine chlorhydrate and acetylsalicylic acid, on thalamic mast cell numbers in rat

Thalamic mast cells (TMCs), the only immunocytes known to infiltrate the brain in physiological conditions, respond to pharmacological agents including sumatriptan - a serotonergic anti-migraine agent - that increases their number. We analysed the effects of two other main analgesics: morphine chlorhydrate, a micro opioid agonist, and acetylsalicylic acid (ASA), a non-steroidal anti-inflammatory drug. All three drugs have specific modes of action, and morphine and ASA, unlike sumatriptan, are also known to interact with peripheral mast cells. Only ASA was effective in promoting TMC number decrease. TMCs, unlike other mast cells, do not express cyclooxygenase (COX) - the key enzyme in the production of prostanoids and the main site of action of ASA - thus dismissing a direct local cellular COX-mediated action. Direct TMC COX-independent mechanisms or effects mediated via distant populations of COX-positive cells such as platelets, leptomeningeal, endothelial and peripheral mast cells are thus probable. ASA, morphine and sumatriptan have distinct TMC effects, suggesting that the TMC number variations they induce are more likely to derive from systemic vasoactive actions than from pharmacological mechanisms devoted to pain relief.

Chronic daily intrathecal injections of a large volume of fluid increase mast cells in the thalamus of mice

Mast cells are found in the central nervous system (CNS) as well as in the periphery. In the brain of mice, they are localized primarily in the thalamus and meninges. Although their numbers increase in response to stress, the mediator of their recruitment is not known. During studies in which drugs were delivered intrathecally in a volume sufficiently large to distribute to the brain, we discovered that repeated daily injections of this large volume increased the number of mast cells in the thalamus. The increase was not due to changes in electrolyte composition of the cerebrospinal fluid (CSF) as chronically administered artificial CSF produced similar effects. Repeated injections of even small volumes (2 mul) increased mast cells in the medial intralaminar (Med), ventral posterior (VP) and posterior (Po) nuclei. Increasing the volume injected daily to 20 mul increased mast cells in the lateral intralaminar (Lat), laterodorsal (LD), ventrolateral (VL) and lateral geniculate (LG) nuclei and further increased those in the lateral extension of the Po nucleus. Thus, small and large volumes augment distinct populations of mast cells. While stem cell factor (SCF) is abundant in the CNS and is chemotactic to mast cells in the periphery, thalamic mast cells in the rodent do not express c-kit, the SCF receptor, suggesting that this factor may not be responsible for the effect. Consistent with this, centrally injected SCF was incapable of increasing thalamic mast cell populations after either single or chronic (21 days) daily injections compared to the effect of saline alone. Although the mechanism is not known, repeated injections of a large volume of fluid dramatically increase mast cells in the CNS, a phenomenon that may be relevant to clinical conditions of increased CSF pressure or volume.

Traumatic brain injury results in mast cell increase and changes in regulation of central histamine receptors

Experimental fluid-percussion models produce brain injury by rapidly injecting saline into the closed cranium of rats. In this study our purpose was to determine how the central histaminergic system, which controls excitability and neurotransmitter release through G-protein coupled receptors, is affected by the pathophysiology of traumatic brain injury. We found that mast cell infiltration, as a result of the trauma, occurred primarily in the injured cortex and did not proceed beyond the fimbria of the hippocampus. In comparing injured animals with controls we found that H3 receptor binding densities are significantly decreased bilaterally in the cortex but are significantly increased bilaterally in the thalamus. H3 receptor binding densities may well be affected by mast cell secretion of mediators (i.e. histamine, heparin, leukotrienes), evidenced by detection of a cosecreted enzyme (mast cell tryptase) in the extracellular region. Moreover, we detected significant decreases in H1 and H3 receptor mRNA as well as Cu/Zn-dependent superoxide dismutase (SOD) mRNA in the thalamic region closest to the trauma. These significant decreases delineate the extent of cellular damage because of trauma and may underlie sustained cognitive and motor deficits displayed by these animals.

Evidence for serotonin influencing the thalamic infiltration of mast cells in rat

Serotonin (5-HT) is involved in neuroimmunomodulation. We analyzed the effects of sumatriptan, a 5-HT(1B/1D) receptor agonist, and ondansetron, a 5-HT(3) receptor antagonist, on thalamic mast cell (TMC) population, the only immunocytes known to infiltrate the brain in physiological conditions. Only sumatriptan was effective, significantly increasing TMC numbers versus controls, and especially those containing 5-HT. 5-HT(1B) receptors are concentrated in the median eminence on non-serotonergic axonal endings, probably hypothalamic terminal fibers, involved in hypothalamic-pituitary neuroendocrine modulating processes. TMC variations could reflect serotonergic actions on these fibers. TMCs would thus be cellular interfaces mediating immune action in the nervous system in relation with the hormonal status of the organism.

Unilateral spinal nerve ligation leads to an asymmetrical distribution of mast cells in the thalamus of female but not male mice

Mast cells are restricted to the leptomeninges and thalamus of healthy mice. These populations are increased by stress and highly sensitive to reproductive hormones. To examine the influence of nociception, a form of stress, on thalamic mast cells, we ligated the left fifth lumbar spinal nerve of male and female mice to induce hyperalgesia. Two, 7 and 14 days later, mice were killed and thalami examined histologically using toluidine blue stain. The total number of thalamic mast cells was not influenced by ligation of the spinal nerve compared to sham-operation in either female or male mice. However, in females, the percent of thalamic mast cells located on the side of the thalamus contralateral to the ligation was greater on days 2 and 7, coincident with mechanical hyperalgesia. At these times, areas in which mast cells were most dense contralateral to nerve-injury included the posterior (Po) and lateral geniculate (LG) nuclei compared to their symmetrical distribution in sham-operated mice. These data suggest that local nociceptive signals to each side of the thalamus rather than stress hormones influence the location of mast cells during the development of allodynia and hyperalgesia. In addition, both hyperalgesia and mast cell distribution induced by nerve-ligation differ in females compared to males, reflecting a novel neuroimmune response to pain within the CNS.

Selective response of various brain cell types during neurodegeneration induced by mild impairment of oxidative metabolism

Age-related neurodegenerative diseases are characterized by selective neuron loss, glial activation, inflammation and abnormalities in oxidative metabolism. Thiamine deficiency (TD) is a model of neurodegeneration induced by impairment of oxidative metabolism. TD produces a time-dependent, selective neuronal death in specific brain regions, while other cell types are either activated or unaffected. TD-induced neurodegeneration occurs first in a small, well-defined brain region, the submedial thalamic nucleus (SmTN). This discrete localization permits careful analysis of the relationship between neuronal loss and the response of other cell types. The temporal analysis of the changes in the region in combination with the use of transgenic mice permits testing of proposed mechanisms of how the interaction of neurons with other cell types produces neurodegeneration. Loss of neurons and elevation in markers of neurodegeneration are accompanied by changes in microglia including increased redox active iron, the induction of nitric oxide synthase (NOS) and hemeoxygenase-1, a marker of oxidative stress. Endothelial cells also show changes in early stages of TD including induction of intracellular adhesion molecule-1 (ICAM-1) and endothelial NOS. The number of degranulating mast cells also increases in early stages of TD. Alterations in astrocytes and neutrophils occur at later stages of TD. Studies with transgenic knockouts indicate that the endothelial cell changes are particularly important. We hypothesize that TD-induced abnormalities in oxidative metabolism promote release of neuronal inflammatory signals that activate microglia, astrocytes and endothelial cells. Although at early stages the responses of non-neuronal cells may be neuroprotective, at late phases they lead to entry of peripheral inflammatory cells into the brain and promote neurodegeneration.

Ultrastructural evidence of brain mast cell activation without degranulation in monkey experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an animal model for the human demyelinating disease multiple sclerosis (MS). Increased permeability of the blood-brain barrier (BBB) precedes the development of clinical or pathologic findings in MS and may be induced by perivascular brain mast cells secreting vasoactive and proinflammatory molecules. Brain mast cells were investigated ultrastructurally in acute EAE of the non-human primate common marmoset Callithrix jacchus, which develops a mild neurologic relapsing-remitting course. Control diencephalic samples contained perivascular mast cells with mostly intact electron dense granules. In contrast, EAE samples had marked demyelination and mast cells with numerous altered secretory granules; their electron dense content varied in amount and texture with a "honeycomb" or "target" appearance, but without degranulation. These changes were evident even before the development of any clinical symptoms and suggest that brain mast cells may be involved in EAE, and possibly MS, through a unique process that may involve selective secretion of molecules able to disrupt the BBB.

Increase of rat medial habenular mast cell numbers by systemic administration of cyclophosphamide

Cyclophosphamide administration generates systemic toxicity having immune and nervous consequences. After focusing on nervous consequences by studying neuronal activity, we now consider cyclophosphamide impact on diencephalic mast cells as part of the brain immune system. Diencephalon, the ultimate sensory relay before neocortical processing, is the only brain structure containing mast cells. Single cyclophosphamide administration (100 mg/(kg 1 ml ip)) was performed in naturally behaving rats and diencephalic mast cell numbers were analyzed once all drug effects had developed (4 h postinjection). Significant increases were observed only in the medial habenular nucleus--bilaterally and especially in its caudal portion. Mast cell increase is temporally related to behavioral impairment and evoked neuronal activity in a restricted number of visceral/limbic extrathalamic structures. The medial habenular nucleus belongs to the limbic system involved in processing emotional reactions and regulation of the autonomic nervous system. Its involvement during toxic challenge is highly compatible with its presumed function in the maintenance of vital functions.

Mast cells: new targets for multiple sclerosis therapy?

Growing evidence suggests that mast cells (MCs) play a crucial role in the inflammatory process and the subsequent demyelination observed in patients suffering from multiple sclerosis (MS). Although no consensus exists on the role of mast cells in multiple sclerosis, recent results from animal models clearly indicate that these cells act at multiple levels to influence both the induction and the severity of disease. In addition to changing our views on the pathophysiology of multiple sclerosis, the concept that mast cells are critical for the outcome of the disease could have an important impact on the development of new therapeutic approaches.

Depletion of brain histamine produces regionally selective protection against thiamine deficiency-induced lesions in the rat

Breakdown of the blood brain barrier and the subsequent accumulation of free radicals, lactate, and glutamate appear to be the immediate causes of thiamine deficiency (TD)-induced damage to thalamus. The mechanisms triggering these events are unknown but recent evidence suggests an important role of histamine. We therefore studied the effects of histamine depletion on thalamic lesions in the pyrithiamine-induced thiamine deficient (PTD) rat. Chronic intracerebroventricular (i.c.v., 7 days) infusion of alpha-fluoromethylhistidine (FMH), combined with bilateral ibotenate destruction of the histamine-containing neurons in the tuberomammillary (TM) nucleus and bolus i.c.v. infusion of 48/80, a potent mast cell degranulating agent, was used to deplete brain histamine levels. PTD rats receiving combined FMH + 48/80 + TM lesions developed acute neurological symptoms, including spontaneous seizures, approximately 1 day earlier than PTD rats treated with i.c.v. infusion of vehicle and sham lesions of the TM. When examined 1 week after restoration of thiamine, the PTD vehicle + sham lesion animals contained severe neuronal loss and gliosis in midline, intralaminar, ventral, lateral, and posterior nuclei. PTD animals treated with FMH + 48/80 + TM lesions had little evidence of neuronal loss or microglial proliferation in thalamus except in the gelatinosus and anteroventral nuclei, in which there was complete neuronal loss. These data demonstrate a significant and regionally selective role of histamine in the development of thalamic lesions in a rat model of Wernicke's encephalopathy. Furthermore, these data suggest either a dissociation between seizures and thalamic lesions or a significant role of histamine in seizure-related damage to the thalamus.

Stimuli from conspecifics influence brain mast cell population in male rats

It is well established that mast cells occur within the brain of many species, and that the brain mast cell population is not static, but changes with the behavioral and physiological state of the animal. In this study, we tested whether exposure to conspecifics alters the number of brain mast cells in male rats, and then investigated the nature of stimuli influencing the changes observed in the number and localization of brain mast cells. Five days of cohabitation with an ovariectomized, estrogen-progesterone (OVX + EP)-treated female resulted in the largest number of thalamic mast cells, while pairing with such a female physically separated by a wire mesh or with a novel male produced a smaller, but significant increase over other pairings (OVX females for 5 days, OVX and OVX + EP females for 1 day, familiar or isolated males for 5 days). In all groups, mast cells were localized within specific dorsal thalamic nuclei, including the paraventricular nucleus, anterior nuclear group, or mediodorsal, ventroposterior, or medial geniculate nuclei. The results suggest that the behavioral and/or endocrine factors associated with cohabitation with conspecifics are sufficient to alter the number of brain mast cell-specific nuclei in the thalami of male rats and thus can provide targeted delivery of neuromodulators to specific regions of the brain that process information concerning the normal physiological state of the animal.